1. Field of the Invention
The present invention relates to semiconductor devices. More particularly, the present invention relates to an internal reference voltage generator and an internal power supply voltage generator in semiconductor devices.
2. Description of the Related Art
In conventional semiconductor devices, particularly, in semiconductor memory devices, in order to provide stable, low power operation, an internal power supply voltage is generated from an external power supply voltage and is used as a power supply source for each of the circuits on a chip. For semiconductor devices, the current in a transistor varies according to variations in temperature, and thus the performance of circuits having transistors fluctuates. For example, during a temperature increase, carrier mobility of a transistor decreases during strong inversion, thereby reducing the current and the operating speed of the circuitry.
In order to reduce such fluctuations in the performance of semiconductor devices caused by variations in temperature, a conventional internal power supply may include a feature wherein an output supply voltage is increased at a higher temperature, thereby increasing current through the chip transistors, and the output supply voltage is decreased at a lower temperature, with attendant decreased current. Thus, the current in a transistor may be maintained constant and independent of variations in temperature.
In one such approach, a band-gap reference generator has been used to vary an internal power supply voltage according to changes in temperature. FIG. 1 illustrates a conventional band-gap reference generator, wherein a reference voltage VREF is provided to a circuit for generating an internal power supply voltage. The band-gap reference generator shown in FIG. 1 is able to arbitrarily adjust and control a temperature coefficient of reference devices on a chip, and thus is able to vary the value of the reference voltage VREF as a function of temperature. Disadvantageously, a variation in the reference voltage VREF may be significantly larger than normal variations in an external power supply voltage EVDD.
In an alternate approach that does not use a reference voltage variation as discussed above, a complementary metal oxide semiconductor (CMOS) reference voltage generator is used instead of a band-gap reference generator to provide for stable voltage operation that is independent of changes in the external power supply. FIG. 2 illustrates such a conventional CMOS reference voltage generator. The CMOS reference voltage generator shown in FIG. 2 is insensitive to variations in the external power supply voltage EVDD and has a stable operation but disadvantageously cannot arbitrarily control the temperature dependency in the associated circuitry.
FIG. 3 illustrates a circuit diagram of a conventional internal power supply voltage generator. Referring to FIG. 3, the conventional internal power supply voltage generator includes an internal reference voltage generator 31 for receiving a reference voltage VREF and generating an internal reference voltage VREFP, a comparator 33 for comparing the internal reference voltage VREFP with an internal power supply voltage IVDD, and a driver 35 for receiving an external power supply voltage EVDD in order to generate and output the internal power supply voltage IVDD. The reference voltage VREF is a voltage that may be derived from the band-gap reference generator shown in FIG. 1 or the CMOS reference voltage generator shown in FIG. 2. The internal reference voltage generator 31 includes a differential amplifier 31a, a first resistor R1, and a second resistor R2. The internal reference voltage generator 31 generates the internal reference voltage VREFP according to the ratio of the resistors R1 and R2 and the reference voltage VREF. The internal reference voltage VREFP may be determined by the equation:
VREFP=VREF(1+R1/R2)xe2x80x83xe2x80x83[1]
and is not sensitive to manufacturing processes and temperature.
Since the foregoing conventional internal power supply voltage generator is insensitive to temperature, the value of the internal reference voltage VREFP cannot be controlled by changes in temperature. As a result, the value of the internal power supply voltage IVDD also cannot be controlled by changes in temperature.
To solve the above problems, it is a first feature of an embodiment of the present invention to provide an internal reference voltage generator in a semiconductor device, which is capable of controlling the value of an internal reference voltage according to changes in temperature.
It a second feature of an embodiment of the present invention to provide an internal power supply voltage generator in a semiconductor device, which is capable of controlling the value of an internal power supply voltage according to changes in temperature.
It is a third feature of an embodiment of the present invention to provide a temperature-compensating reference voltage generator, including a temperature-compensating voltage divider for dividing an input reference voltage in order to generate a temperature-compensated output voltage at an output node of the voltage divider.
In order to implement the first feature, according to a first embodiment of the present invention, an internal reference voltage generator in a semiconductor device preferably includes a first differential amplifier for differentially amplifying a first reference voltage input into a first input terminal of the differential amplifier and an input voltage input into a second input terminal of the first differential amplifier in order to output an internal reference voltage to an output terminal of the first differential amplifier; a first resistor connected between the output terminal of the first differential amplifier and the second input terminal of the first differential amplifier; and a second resistor connected between a second reference voltage and the second input terminal of the first differential amplifier, the first and second resistors forming a first voltage divider. The impedance of the first resistor is preferably dynamically varied by a voltage that may be varied according to changes in temperature. Since variable impedance devices are typically implemented using active devices, it is preferable that the first resistor consists of one or more PMOS transistors, the gates of which are controlled by voltages that are varied according to the temperature.
In order to implement the first feature, according to a second embodiment of the present invention, an internal reference voltage generator in a semiconductor device preferably includes a first differential amplifier for differentially amplifying a first reference voltage input into a first input terminal of the first differential amplifier and an input voltage input into a second input terminal of the first differential amplifier in order to output an internal reference voltage to an output terminal of the first differential amplifier; a first resistor connected between the output terminal of the differential amplifier and the second input terminal of the first differential amplifier; and a second resistor connected between a second reference voltage and the second input terminal of the first differential amplifier, the first and second resistors forming a first voltage divider. The impedance of the second resistor is preferably dynamically varied by a voltage that is varied according to changes in temperature.
It is preferable that the second resistor consists of one or more NMOS transistors and that the voltages of gates of the NMOS transistors be varied according to the temperature. It is also preferable that the internal reference voltage generator further includes a temperature-compensating variable voltage generator for generating the reference voltage, which may be varied according to changes in temperature.
It is also preferable that the temperature-compensating variable voltage generator includes a second differential amplifier for differentially amplifying a third reference voltage input into a first input terminal of the second differential amplifier and a voltage input into a second input terminal of the second differential amplifier in order to output an output voltage to an output terminal of the second differential amplifier, a third resistor connected between the output terminal of the second differential amplifier and the second input terminal of the second differential amplifier, a fourth resistor connected between the second reference voltage and the second input terminal of the differential amplifier, and a variable voltage generator for generating the voltage varied according to changes in temperature in response to the output voltage of the differential amplifier and the third reference voltage. The third and fourth resistors form a second voltage divider.
In order to implement the second feature, according to a third embodiment of the present invention, an internal power supply voltage generator in a semiconductor device preferably includes an internal reference voltage generator for generating an internal reference voltage that may be varied according to changes in temperature; a comparator for comparing the internal reference voltage with an internal power supply voltage; and a driver for receiving an external power supply voltage in order to output the internal power supply voltage in response to an output signal of the comparator.
In order to implement the third feature, according to a fourth embodiment of the present invention, the temperature-compensating reference voltage generator having the temperature-compensating voltage divider is provided, wherein the temperature-compensating voltage divider preferably includes at least a first electronic element having a first output impedance that exhibits a positive temperature coefficient and at least a second electronic element having a second output impedance that exhibits a negative temperature coefficient, the first and second electronic elements being combined such that a change in the temperature-compensated output voltage is a function of a change in temperature. The first electronic element may be a PMOS transistor and the second electronic element may be an NMOS transistor, in which case the PMOS transistor should operate in a weak inversion region and the NMOS transistor should operate in a strong inversion region. In the fourth embodiment, the change in the temperature compensated output voltage is either directly or inversely proportional to a change in temperature.
Another feature of the present invention is implemented by a fifth embodiment of the present invention that provides a temperature compensating power supply, including: a temperature-compensated reference voltage, which is generated from at least two reference voltages and a regulating element for generating an output voltage from an input voltage under control of the temperature-compensated reference voltage and characterized in that the output voltage rises with increased temperature and falls with decreased temperature. Alternatively, in a sixth embodiment of the present invention, the output voltage falls with increased temperature and rises with decreased temperature.
Preferably, in the fifth and sixth embodiments, at least one of the two reference voltages is a temperature-compensated reference voltage. Preferably, the temperature-compensated reference voltage is generated using at least one transistor operating in a weak inversion region and at least one transistor operating in a strong inversion region. In some cases, the two reference voltages are about the same or the same.
These and other features of the present invention will be readily apparent to those of ordinary skill in the art upon review of the detailed description that follows.